Interpolymerization of ethylene-propylene monomers

ABSTRACT

THE INTERPOLYMERIZATION OF ETHYLENE AND PROPYLENE ALONE OR WITH OTHER DIFFERENT MONOMERS COPOLYMERIZABLE THEREWITH IN THE PRESENCE OF A ZIEGLER POLYMERIZATION CATALYST TO FORM A SOLID POLYMER. THE ETHYLENE AND PROPYLENE MUST BE PRESENT IN RELATIVE PROPORTIONS RANGING BETWEEN 10:90% AND 90:10% BY WEIGHT. PREFERRED ZIEGLER CATALYSTS ARE THOSE FORMED BY MIXING AN ORGANO-METAL COMPOUND, SUCH AS AN ORGANO ALUMINUM COMPOUND, AS FOR EXAMPLE, AN ALUMINUM TRIALKYL, OR AN ALUMINUM ALKYL HALIDE WITH A COMPOUND SUCH AS A SALT OF A METAL OF GROUP IV-B, V-B, OR VI-B OF THE PERIODIC SYSTEM, INCLUDING THORIUM AND URANIUM.

K. ZIEGLER ET AL Sept 3 V I INTEBROLYMERIZATION OF ETHYLENE-PROPYLENEIONOMERS 2 Sheets-Sheet 1 Original Filed June 8. 1955 qmmmn w 2.3 Er3:23 ham 25 5 5d: 52* magma moi-a3 Sept. 3, 1974 K. ZIEGLER ET ALINTERPQDYMERIZATION OF ETHYLENE-PROPYLENE HONOMERS Original Filed June8, 1955 2 Sheets-Sheet 2 A COPOLYNERISATE MucH H0, LITTLE H US. Cl.26088.2 9 Claims ABSTRACT OF THE DISCLOSURE The interpolymerization ofethylene and propylene alone or with other different monomerscopolymerizable therewith in the presence of a Ziegler polymerizationcatalyst to form a solid polymer. The ethylene and propylene must bepresent in relative proportions ranging between 10:90% and 90:10% byweight. Preferred Ziegler catalysts are those formed by mixing anorgano-metal compound, such as an organo aliuninum compound, as forexample, an aluminum trialkyl, or an aluminum alkyl halide with acompound such as a salt of a metal of Group IV-B, VB, or VI-B of thePeriodic System, including thorium and uranium.

This application is a continuation of our copending application Ser. No.514,068, filed June 8, 1955, now Pat. 3,342,358.

This invention relates to a process for polymerizing unsaturatedhydrocarbons of the formula CH =CHR in which R is a saturated aliphaticradical, an alicyclic radical or an aromatic radical and morespecifically an alkyl, cycloalkyl or aryl radical, alone, in mixtureswith each other, or in mixtures with other different monomerscopolymerizable therewith.

The unsaturated hydrocarbons of the stated formula may be regarded asalpha-olefins this term being used in a broad sense and includingstyrene.

The pending application of one of us, Karl Ziegler, Ser. No. 469,059,filed Nov. 15, 1954, now Pat. No. 3,257,332, issued June 21, 1966,describes a method for polymerizing ethylene to high polymers using, asreaction initiators, catalysts obtained by the reaction of certaincatalytic heavy metal compounds with certain catalytic metal alkylcompounds, in the dissolved state.

The polymerization of ethylene in contact with these catalysts resultedin the production of polyethylenes having molecular weights as high as300,000 to 2,000,000 as described in said pending application, supra.

However, it is not apparent from the work with ethylene that the same orsimilar catalysts would be useful in the production of high molecularweight polymers of the alpha-olefins as defined in the formula givenhereinabove.

The usefulness of a catalyst as initiator for the polymerization ofhigher homologues of ethylene cannot be predicated on, or assumed from,the usefulness thereof as initiator of ethylene polymerization. Pastexperience has shown that when ethylene homologues, such as propylene,were polymerized in the presence of various catalysts that had been usedin the production of polyethylene of relatively high molecular weight,only low polymers of the propylene, (usually dimers, trimers andtetramers in the form of light oils or somewhat higher polymers in theform of more or less viscous lubricating oils having rela- States Patenttively low average molecular weights) were obtained in satisfactoryyields.

The polymers of the ethylene homologues obtained by the processes knownin the art consist of mixtures of homologues and of variously branchedisomers. The higher the temperature used, the smaller the degree ofpolymerization. But even when carrying out the known processes atrelatively low temperature, the products of a somewhat higher molecularweight thus obtained are still mainly liquids or liquids in admixturewith amorphous solids.

One object of this invention is to provide a new process for theproduction of alpha-olefin polymers and copolymers.

Another object of the invention is to provide a new process for theproduction of alpha-olefin polymers and copolymers of high molecularweight.

A further object is to provide a new process for polymerizingalpha-olefins and mixtures containing them at moderately elevatedtemperatures to obtain high molecular weight, long chain polymers andcopolymers.

A specific object is to provide a process for producing plastic,moldable propylene polymers and copolymers.

Still another specific object is to produce copolymers of thealpha-olefins according to the aforesaid general formula with othermonomers, in particular with ethylene, in which copolymers thepolyethylene component greatly predominates.

Unexpectedly, we have found that high molecular weight, plastic moldablehomopolyrners of the alphaolefins and copolymers thereof with each otheror with others monomers copolymerizable therewith, can be obtained bycarrying out the polymerization or copolymerization in the presence ofcatalysts of the type described in the pending Ziegler application,supra, as initiators of the polymerization of ethylene, if thecomponents used in preparing the catalysts are used in a controlledmolar ratio.

These reactants are (A) a heavy metal compound and (B) a reducing agentfor the heavy metal compound.

As (A) there are used heavy metal compounds other than heavy metaloxides either dry or hydrated, of a subgroup of groups IV to VI of thePeriodic Table, i.e., compounds of the elements of titanium, zirconium,hafnium and thorium in Group IV, vanadium, tantalum and columbium inGroup V, and chromium, molybdenum, tungsten and uranium in Group VI.

Various compounds of the metals may be used, for instance salts such ashalides, e.g. chlorides and bromides, oxyhalides, such as theoxychlorides, complex halides, for instance, complex fluorides, forexample, complex fluorides of titanium corresponding to the formulaMeTiHal in which Me is the metal and Hal is halogen and a specificexample of which is potassium titanium fluoride (K TiF metallo-organiccompounds and other organic derivatives such as alcoholates, acetates,benzoates, acetyl acetonates or the like.

The reducing agent (B) for the heavy metal compound contains at leastone metal selected from the metals of Groups II and III of the PeriodicTable. As the reducing agent there may be used metal alkyl, alkoxyandarylcompounds which comprise a substance or mixture of substances fromthe group of simple and complex compounds the molecules of whichcontain, as a central atom, an element from Group II of the Table, i.e.,beryllium, magnesium, zinc, cadmium and other elements of Group II, aswell as boron, aluminum and other elements of Group III of the Table.The valences of the aforesaid central atom of these metal alkylcompounds may all be linked to the same or different alkyl, alkoxy, arylor aryloxy radicals, such as ethyl, propyl, butyl, ethoxy, phenyl,

phenoxy, etc., or at least one valence of the central atom may besatisfied by a halogen or hydrogen.

The reducing agent may also be an alkali metal or alkaline earth metal,e.g., sodium or calcium, alloys of these metals, hydrides of the metalsor mixtures of the metals or hydrides. The reducing agent may also be acomplex of the metal hydrides mentioned with any one of the aforesaidmetallo-organic compounds of metals of Groups II and III of the PeriodicTable including those containing halogen or hydrogen, as well asaluminum hydrides, boron hydride, boron alkyl or boron aryl compounds,or alkyl or aryl esters of boric acid.

Preferred reducing agents are those having the general formula R!RIIAIRIII in which R' and R" each represent a hydrocarbon radicalpreferably an alkyl radical, and R" represents a hydrocarbon radical,hydrogen, halogen or an alkoxy group.

Other suitable reducing agents have the general formula in which A is analkali metal, R and R" are hydrocarbon, particularly alkyl, radicals andX and Y are hydrogen, halogen or hydrocarbon radicals.

The polymerization catalysts may be obtained by reacting the heavy metalcompound and reducing agent together in an inert solvent or diluent(i.e. a liquid which does not affect the composition of the polymerformed) in the absence of water and oxygen. It appears that theparticular reducing agent used with the heavy metal compound is notcritical so long as the heavy metal compound is not an oxide, in whichcase higher polymerization temperatures would be required, resulting inproducts of lower average molecular weight.

In general, polymerization catalysts obtained by reacting the heavymetal compound other than oxide with aluminum compounds of formula [I]or [II] are preferred. Those catalysts can be produced as required in -avery simple manner; and when they are used polymerization of thealpha-olefin or of mixtures of copolym- -erizable monomers containingthe alpha-olefin proceeds particularly smoothly. However, compounds ofFormulae I and II in which the aluminum is replaced by magnesium or zincare also very suitable for use as the reducing agent.

Particularly preferred catalysts are those obtained by reactionof'titanium or zirconium tetrachloride or other halides of the metalswith aluminum alkyls, especially aluminum triethyl or diethyl aluminumchloride as the reducing agent. Equally satisfactory results areobtained using titanium or zirconium compounds such as theirtetrachlorides reduced by aluminum trioctyl, dipropyl aluminum fluoride,aluminum tri-isobutyl, aluminum di-isobutyl hydride, ethoxy-diethylaluminum, sodium aluminum tetraethyl, and lithium aluminum di-isobutyldihydride.

It is advantageous to prepare the polymerization catalyst by grindingthe heavy metal compound and reducing agent together in a ball-type millor in a triturator of the ball-type. For example, zirconiumtetrachloride is difiic-ultly soluble in hydrocarbons such as thesaturated aliphatic hydrocarbons suitable for use as the inert solvent,and may become coated, during the reaction, with an impenetrable ordifiicultly penetrable crust of the reducing agent. Such crust orcoating is continuously removed, as it is formed in the process, by thegrinding to which the mass is subjected in the ball mill.

As indicated above, for the rapid polymerization of the alpha-olefin orcopolymerizable mixtures containing them, the heavy metal compound andreducing agent are used in molar ratios that are controlled andcritical. Such ratio influences both the rate or velocity of thepoly-merization and the molecular weight of the products. In

general, the heavy metal compound and reducing agent are used in a molarratio between 1:1 and 1:12. Specific molar ratios in the range statedmay be preferred for particular heavy metal compounds and reducingagents. For instance, when the reducing agent is other than a metaltrialkyl such as aluminum trialkyl, for instance when it is dialkylaluminum chloride, the molar ratio of the reducing agent to heavy metalcompound such as titanium tetrachloride, zirconium tetrachloride, etc.,is preferably about 2: 1.

When aluminum trialkyl is used as the reducing agent, the catalystsobtained yield polymers of higher molecular weight when, in the mixtureof aluminum trialkyl and heavy metal compound from which the catalyst isprepared, the aluminum trialkyl predominates.

In preparing the catalyst from, say, magnesium or zinc alkyls, the ratioof the reducing agent to heavy metal compound is adjusted according tothe different valences of the metals involved.

The polymerization is carried out at a temperature of 30-70 C. in thepreferred practice of the invention. Higher temperatures up to 150 C.may be used. However, high temperatures are not usually required sinceheavy metal oxides are not employed. The polymerization may be allowedto proceed at normal atmospheric pressure, or under an increasedpressure of 5 to 25 atmospheres.

The following examples are given to illustrate specific embodiments ofthe invention, it being understood that these examples are not intendedas limitative.

In copolymers produced according to the invention, either thealpha-olefin or the other monomer or monomers may predominate in thecopolymer molecule. Thus, we have produced copolymers of propylene andethylene containing, by weight in the polymer molecule, 10% of propyleneand of ethylene. We have also produced copolymers containing, in thepolymer molecule, 30% of isobutylene and 70% of ethylene. Copolymerscontaining, in the polymer molecule, 50% of propylene and 50% ofethylene have been prepared by the method described herein. Copolymerscontaining up to 70% ethylene and up to 30% propylene are contemplated.

EXAMPLE I About 4.75 gms. of titanium tetrachloride are introduced intoa solution of 5.7 gms. triethyl aluminum in 250 ml. of a Fischer-TropschDiesel oil (suitably freed, by hydrogenation, of unsaturatedconstituents and successively distilled over sodium) with stirring andunder a nitrogen atmosphere. Agitation is continued for one hour at roomtemperature. A suspension of a brown-black substance in the Diesel oilis formed. The suspension of the catalyst thus obtained is introduced,with stirring into a 5 liter autoclave filled with nitrogen andcontaining 1.0 liter of the Diesel oil, and 600 gms. of dried, air-freepropylene are pumped in. The temperature is raised to 70 C., stirringbeing continued, whereupon the pressure increases to a maximum of 21atm. Within 72 hours, the pressure decreases to 11.0 atm. The unreactedpropylene is then released from the warm autoclave and 225 gms.propylene are recovered. The solid polypropylene occurs in a pastelikesuspension in the Diesel oil. The suspension is somewhat dark in colordue to the presence of portions of the catalyst therein. The solvent isremoved from the polypropylene by suction, and the polymer is then freedof Diesel oil by Washing with acetone. The polymer is then decolorizedby heating it under stirring, with methanolic hydrochloric acid. Thecolorless polypropylene is washed under suction with water to remove thehydrochloric acid, then with acetone to remove the bulk of the moisture,and finally dried.

An additional quantity of the polypropylene is recovered from the Dieseloil mother liquor by precipitation with acetone, and may be processed asdescribed. A total yield of 338 gms. of granular polypropylene isobtained.

The solid, granular polypropylene may be pressed at 140 C. to obtainflexible sheets or films which appear transparent in thin films andopaque in thick layers. Th1s propylene polymer is distinguished by avery characteristic infra-red spectrum, illustrated by FIG. 1 of theappended drawing.

EXAMPLE II Example I is repeated, except that the propylene is replacedby an equivalent amount of alpha-butylene or of a C -hydrocarbon rich inalpha-butylene. The poly-n-butylene obtained resembles the polypropyleneof Example I in appearance but is somewhat softer.

EXAMPLE III Example I is repeated, except that an ethylene partialpressure of 1-3 atm. is maintained in the autoclave by connecting thelatter with an ethylene cylinder and by carefully adjusting the valve.Because ethylene polymerizes more rapidly than propylene, thecomposition of the liquid phase is appropriately controlled by takingsmall samples and by gas analysis; to maintain an amount of ethylene inthe liquid which is only a few percent (up to of the propylene. A solidcopolymer is obtained. It may be formed into foils having propertiesbetween those of film-forming polyethylene and polypropylene.

EXAMPLE IV The catalyst (prepared from 3.5 g. diethyl aluminum chlorideand 0.44 g. titanium tetrachloride) is dissolved in 2.5 1. Diesel oilunder an atmosphere of nitrogen, and a dried, oxygen free gaseousmixture of 12 vol. percent propylene and 88 vol. percent ethylene isintroduced under atmospheric pressure. The vessel is heated to about 70C. and then, within 8 hours, the temperature is gradually raised to 90C. A finely powdered, insoluble polymer separates, whereupon thecontents of the vessel become progressively thicker. The reaction isstopped after 8 hours. About 168 g. of a solid, colorless copolymer ofethylene and propylene is separated by filtration. That the product is acopolymer is shown by the infra-red spectrum. The spectrum of thecopolymer was compared with that of an ethylene homopolymer obtained insimilar manner. In the range 1382 CI1'1."1 there appears for thecopolymer an additional absorption band (indicated by the mark-x-in theabsorption spectrum of the copolymer, FIG. 2 of the drawing) which ischaracteristic of methyl branching. The production of the copolymer isalso evidenced by careful quantitative determination of the amounts ofethylene and propylene in the gases released from the reaction vesseland condensed by cooling. It is thus readily ascertained that about 10%by weight propylene is contained in the polymer molecule.

EXAMPLE V product having a thickness of 120-140 microns shows aninfra-red absorption band at 658 cm." which is not found in theinfra-red spectrum of the similarly prepared homopolymer, polyethylene.Said band is characteristic of the double bond in cyclohexene ring. Thisinfra-red absorption is not due to the presence of residual portion ofvinylcyclohexene dissolved in the polymer, but is due to acceptance ofthe vinylcyclohexene into the polymer molecule, as shown by the factthat the infra-red absorption spectrum of the polymerizate does not showthe very characteristic band of the vinyl group initially present in theunpolymerized vinylcyclohexene molecule. A copolymer is thus obtained,built up of units derived from both ethylene and vinylcyclohexene, theunits derived from ethylene predominating. As compared to polyethylene,the copolymer has distinctly increased strength and a higher softeningtemperature. Apparently, it is moderately crosslinked through branchesformed by the unsaturated cyclohexene side chains.

EXAMPLE VI About 30 ml. of air-free Fischer-Tropsch Diesel oil distilledover sodium and completely saturated by hydrogenation are introducedinto a small (150 ml.) ball mill arranged for working under nitrogen,together with 14.1 g. triethyl aluminum and 11.7 g. zirconiumtetrachloride, and the whole is ground for 24 hours to obtain anintimate mixture. A thick black suspension is obtained. It is mixed with1.0 liter of the same Diesel oil and introduced under nitrogen into a 5liters autoclave equipped with a stirrer. 590 g. of propylene are thenpumped in at room temperature, stirring is commenced, and the autoclaveis heated to C. Within 50 hours the pressure falls from the initial 23atm. down to 14.2 atm. The reaction is interrupted, the autoclave isallowed to cool, and the excess propylene is vented. 190 g. of propyleneare recovered. The mass contained in the autoclave is a thick blackslurry which, after the addition of acetone and filtration undersuction, becomes colorless. The residual catalyst is extracted byheating with alcoholic hydrogen chloride. After repeated washing withacetone and drying, 400 g. of a white, flocculent polypropylene areobtained. The polymer can be easily pressed into foils and rolled into asheet.

EXAMPLE VII The catalyst is prepared from 17.1 g. triethyl aluminum and4.75 g. titanium tetrachloride in 250 ml. Diesel oil, and introduced,together with 1390 g. isobutylene, into a 5-liter autoclave filled withnitrogen and provided with a stirrer. The autoclave is then heated to 40C. and the pressure, initially 5 atmo., is raised an additional 4 atm.by pumping in ethylene. The absorption of ethylene commences at oncewith spontaneous increase of the temperature to 55 C. An ethylenepartial pressure of 4 atm. is maintained. After a total of 6 hours, 143g. ethylene are absorbed. The valve of the ethylene cylinder is thenclosed, and stirring is continued until the pressure drops to only 5atm. After cooling, the excess isobutylene is released. The massremaining in the autoclave is a black slurry. It is diluted withacetone, filtered under suction, thoroughly washed, and furtherprocessed as in Example VI. 216 g. of the copolymer of isobutylene andethylene is obtained, about 60 g. of the isobutylene being copolymerizedas evidenced by the infrared spectrum of the copolymer, which is verydifferent from the spectrum of ethylene homopolymers.

EXAMPLE VIII About 17.5 g sodium hydride-triethyl boron (produced byheating sodium hydride with triethylboron in toluene until the sodiumhydride is dissolved) in 200 ml. of toluene and 7.5 g. titaniumtetrachloride are mixed under nitrogen in an autoclave equipped with astirrer. 500 g. propylene are pumped in, and the autoclave is heated to70-80" C., with stirring of the mass. Within 30 hours, the pressurefalls from 20 atm. down to 11 atm. The product is worked up as inExample VI, with similar results.

EXAMPLE 'IX Proceeding as in Example VI, 23 g. of a coarsely groundmagnesium aluminum alloy of the composition Mg Al are ground for 36hours in cc. of hexane with 8.8 g. of titanium tetrachloride. After the36 hour grinding period, titanium tetrachloride can no longer bedetected in samples of the clarified solution. Propylene is polymerizedin contact with the resulting gray-black catalyst suspension, as inExample VI. From 790 g. propylene, there are obtained 660 g. of plasticpolypropylene, and 130 g. of unreacted monomeric propylene. Thepolymeric propylene is similar to the polymer of Examples -I and VI.

It will be apparent from the foregoing that the invention providesmethods for producing very valuabe and unique polymers and copolymers ofthe higher ethylene homologues. Since, in practicing the invention,various changes and modifications may be made in the detailsexemplified, without departing from the sipirit and scope of theinvention, it is to be understood that it is not intended to limit theinvention except as defined in the appended claims.

What is claimed is:

1. A process which comprises interpolymerizing monomers comprisingethylene and propylene in the relative proportion between about l:90% byweight and 90: by Weight in the' presence of a polymerization catalystformed by mixing an organometal compound selected from the groupconsisting of a metal alkyl alkoxymetal or metal aryl of a metalselected from the group consisting of metals of Groups II and III of thePeriodic System, alkali metals and alkaline earth metals with a compoundother than the oxide of a metal selected from the group consisting oftitanium, zirconium, hafnium, vanadium, tantalum, columbium, chromium,molybdenum, tungsten, thorium and uranium, and recovering the solidpolymer formed.

2. Process according to claim 1 in which said organo metal compound isan organo-aluminum compound.

3. Process according to claim 2 in which said organo aluminum compoundis an aluminum trialkyl and in which said metal compound is a salt.

4. Process according to claim 2 in which said organo aluminum compoundis an alkyl aluminum halide and in which said metal compound is a salt.

5. Process according to claim 1 in which said polymerization catalyst isa catalyst formed by mixing an aluminum trialkyl or an alkyl aluminumhalide with a titanium, zirconium or vanadium salt.

6. Process according to claim 3 in which said monomers comprise ethyleneand propylene in the relative proportion of about 10:90% by weight.

7. Process according to claim 3 in which said monomers comprise ethyleneand propylene in the relative proportion of about 90: 10% by weight.

8. Process according to claim 3 in which said monomers comprise ethyleneand propylene in the relative proportion of about :50%. by weight.

9. Process according to claim 3 in which said monomers comprise ethyleneand propylene in the relative proportion of about :3 0% by weight.

References Cited UNITED STATES PATENTS 2,200,429 5/1940 Perriri 2602,691,647 3/1946 Field 2 6088.2 3,300,459 l/l967 Natta 26088.2 2,710,8546/1955 Seelig 26094.9 D 2,726,234 12/1955 Field et al. 26094.9 D

OTHER REFERENCES Gaylord and Mark: Linear and Stereoregular AdditionPolymers, 1959, p. 214.

JOSEPH L. SCHOFER, Primary Examiner A. L. CLINGMAN, Assistant Examiner

